1. Field of the Invention
The present invention is directed to a magnet system of the type suitable for use in nuclear magnetic resonance tomography devices, wherein a homogeneous magnetic field is required in the examination volume.
2. Description of the Prior Art
A magnet system of the type used in nuclear magnetic resonance tomography devices is described in European Application No. 0 167 059 wherein, for the purpose of homogenizing the magnetic field produced by the magnet system, the walls of the magnet are provided with pockets for receiving iron laminae can be stacked. Such adjustment of the magnetic field, referred to as shimming, can thus be achieved without the use of current-carrying coils. Pockets for receiving the laminae can also be provided at the exterior of the magnet. When viewed from the end of the magnet system, the pockets have a star shape or configuration. The magnet system also has a plastic-lined opening to which the iron laminae can also be secured. The iron laminae compensates for inhomogeneities produced by magnetic returns within the magnet system. The desired homogenization of the magnetic field is achieved by a suitable selection of the shape, size, arrangement and number of the iron laminae.
The position and respective dimensions of the individual laminae are first calculated to achieve the desired correction on the basis of known, mathematical field calculation methods. The computationally identified position for a particular lamina must then be transferred to the physical structure of the magnet system. To perserve the validity of the mathematical calculations, the actual placement of the laminae within the magnet system must be accomplished with extremely tight tolerances, which requires a relatively complex procedure. Failure to observe such precision will result in a magnetic field having undesired inhomogeneities.